The present invention relates to a new and improved method of, and apparatus for, forming a continuous fiber layer of substantially constant weight per unit length.
Generally speaking, the arrangement useful for practicing the teachings of the invention embodies supply means for supplying a fiber and air mixture onto a moving, fiber-separating, perforated surface, with a suction opening arranged beneath and extending over a certain zone or region of such perforated surface.
In Austrian patent application No. A4103/66 it is proposed to prevent an uneven fiber deposition upon a perforated or sieve drum, internally of which there prevail vacuum conditions, by providing a drum-shaped cover-shield having a slot and arranged within the perforated drum. This slotted cover-shield oscillates back and forth beneath the contact or impact zone of the fibers which are supplied onto the surface of the perforated drum. As a result, the fibers are deflected throughout a wide zone of the surface of the perforated drum and are distributed during deposition. Hence, there is realized an evening action in the event of deviations in the fiber supply lasting for a short period of time. The weight and the uniformity of the fiber layer which is formed, with this prior art equipment depends exclusively upon the evenness or regularity of the fiber supply. Variations of the fiber supply which last over longer time intervals cannot be evened-out or compensated.
In U.S. Pat. No. 3,239,890 there is taught to the art equipment for forming a fiber layer of constant thickness. Fibers are supplied by means of an air stream onto a rotating perforated or sieve drum within which there prevails a vacuum. The fiber layer forming on the perforated drum produces a pressure drop between the exterior and interior of the perforated drum, this pressure drop corresponding to the thickness of the deposited fiber layer. These pressure variations are measured and utilized for controlling the rotational speed of the perforated drum as a function of the thickness of the fiber layer. Devices of this type, however, are only suitable if, on the one hand, there are not made any great demands upon the short term evenness or regularity of the fiber layer, and, on the other hand, if the fiber layer is not transferred to a machine reguiring a constant supply speed.
Irregularities in the supply or infeed of the fiber material and in the material removal can be only leveled out or compensated by the aforementioned equipment to a limited degree. Equally, it is not possible to achieve uniform deposition of the fiber material upon the perforated drum. Fiber deposition is more or less random.